In recent years, visible light communication using a visible light as a communication medium has been developed, and a visible light communication apparatus that performs visible light communication by use of a visible light such as an illuminating ray has been proposed in Patent Literature 1 below and the like.
With respect to this conventional visible light communication apparatus, a visible light communication apparatus which superimposes a transmitting signal on a visible light to transmit it operates so as to generate a transmitting signal by performing modulation by the 4-level PPM method (pulse-position modulation) onto an information signal (pulse signal) to be transmitted, to apply the transmitting signal to a light source using an LED to drive the LED, and superimpose the transmitting signal on a visible light irradiated from the LED, to transmit it.
Further, in this visible light communication apparatus, in order to effectively use an ordinary use light source for illumination as a light source of the visible light communication apparatus, at the time of applying a PPM signal to the LED light source for illumination, the LED is continuously lit during a period of a digital value of “0” which is relatively long, and the LED is operated to blink on and off at a shorter frequency by a sub-carrier carrier signal during a period of a digital value of “1” which is short in time, thereby securing necessary illuminance for illumination at the time of transmission in visible light communication.
On the other hand, in recent years, portable terminals such as mobile telephones have become remarkably popular, and most people carry portable terminals with them on a daily basis. Further, because a digital camera available for video recording is normally mounted in this type of portable terminal, users live in an environment where they can routinely photograph with a camera.
Therefore, conventionally, in Patent Literature 2 below, there has been proposed a visible light communication apparatus which photographs a visible light irradiated from a light source for illumination serving as a light source of the visible light communication apparatus that performs visible light communication, that is, an illuminating ray for visible light communication on which an information signal to be transmitted is superimposed with a camera of a portable terminal or the like, and analyzes the photographed image data to extract a data bit string contained in the image data, and demodulates information signal data transmitted from the data bit string.